#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
	long long n;
	while(scanf("%lld",&n)!=EOF)
	{
		long long ans = n/2;
		if(n%2) ans = ans-n;
		printf("%lld\n",ans);
	}
}
